The invention relates to improvements in methods of and in apparatus for making trimmed streams (called fillers) of tobacco or other fibrous material of the tobacco processing industry. More particularly, the invention relates to improvements in methods of and in apparatus for making trimmed streams of tobacco fibers or the like wherein the density of each increment of the trimmed stream matches or closely approximates a desired value.
A cigarette rod is normally obtained by admitting fragments of tobacco leaves into an elongated path wherein the fragments accumulate into a stream which is then advanced lengthwise past a trimming station where the surplus is removed so that the thus trimmed stream constitutes a filler which is ready for draping into a web of cigarette paper or other suitable wrapping material. As a rule, the density of the filler is monitored and the thus obtained signals are used to adjust the rate of admission of fragments of tobacco into the path if the ascertained density of the filler deviates from a desired optimum density. The monitoring operation can involve directing one or more beams of radiation against the advancing filler and ascertaining the intensity of that portion of radiation which has penetrated through the filler. The customary means for advancing the stream and the filler is an endless foraminous belt conveyor which cooperates with a suction chamber to attract the fragments of tobacco and to thus advance the stream and the filler along the respective portions of the path.
The means for monitoring the density of the filler normally employs a source of corpuscular radiation (such as beta rays) which is adjacent the path of the wrapped or unwrapped filler. Thus, each increment of the filler must cover a considerable distance before it reaches the monitoring station so that a relatively long portion of the filler is likely to be defective before the monitoring device detects the defect. Moreover, many makers of rod-shaped smokers' articles and filter rod sections are reluctant to utilize monitoring devices which embody sources of corpuscular radiation because the users of such radiation sources must satisfy stringent and expensive requirements concerning the safety of workmen in the plant which produces plain or filter cigarettes, filter rod sections or other rod-shaped articles of the tobacco processing industry.